3 gig memory switch.
Windows workstation/pro allocates only 2 Mb of memory per process, this mean the bundle memory Physical RAM + virtual.
Practically this mean if your scene needs more, it will likely crash
when using some 1,7 ~ 1,8 Gbytes of memory ( again this is the bundle
of Physical + swaped ) never mind you have 1 or 4 Gigs of RAM in your
systrem.
Reason for that is nobody at MS did think aplications would use more memory.
Since they've been asked to allow aplications to be allocated more memory, they've allowed some OS versions to use a switch that permits to allocate more memory to a single process, as much as 3GB, and that's what the 3GB does.
The swich is there for use in those some OSs,some of the server versions of NT, 2000, and XP, but also XP pro.... though the switch is very picky and in some cases not as stable as one would want it to be, here is working in XP pro, and it really makes a difference to be able or not to render some huge scenes, but some times it has not worked.
In case it were not to work, the way to turn it on is via creating a Dual Boot, one switched, the other unswitched, so, in case it fails, you boot again now unswitched.
Here is how I have it in my XP system (credit goes to alexander bicalho):
Start > Config > Control Panel > System
Go to the Advanced Tab
Click "Settings" in Startup and Recovery
Click "Edit" to edit the options file manually
(It should look similar to this one - each computer is unique):
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)WINDOWS="Microsoft Windows XP
Professional" /fastdetect
Create a copy of the last line, add information between quoted and add the switch to the first line:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)WINDOWS="Microsoft Windows XP
Professional" /fastdetect
multi(0)disk(0)rdisk(0)partition(1)WINDOWS="Microsoft Windows XP
Professional 3GB" /fastdetect 3GB
Change the timeout to something different than 0 if yours is 0 so you> have time to choice among options at boot time.
Save the file and reboot. Choose the 3GB option when rebooting. If it doesn't work, you can reboot again and choose the other option, and your system should work fine. I. This should give VIZ, MAX or any other single process you are running the ability to use up to 3GB of memory, allowing you to render bigger scenes.